The present invention relates to a process of laminating multiple large-layer-count substrates with reliable mechanical and electrical connections.
Multilayer substrates potentially offer the advantages of more efficient use of space in a circuit board design, but require more complex connection capability and circuit modularity. Significant problems exist in aligning, laminating, drilling and plating multilayer substrates, particularly for large-layer-count (LLC) substrates and substrates with high aspect ratios.
LLC substrates require relatively large drills to form via holes for connection to another LLC substrate. Alignment of layers and wandering of the drill bit present serious obstacles to correct registration and connection of the two substrates. Substrates with high aspect ratios introduce additional complications, since it is difficult to plate a via hole to connect multiple substrates without disturbing adjacent circuit features.
Additionally, it is desirable for the LLC substrates to be formed as separate, finished LLC substrates that can be independently tested before attachment to another LLC substrate. The process of electrical interconnection between substrates should also be repairable without damaging the existing construction of each layer and without affecting the precise alignment of layers, to permit repair of open connection between the substrates in question. If the interconnection of substrates is not repairable, as is often the case in existing multilayer substrate processes, the failure of a single connection causes the entire multilayer package of substrates to be incurably defective.
Therefore, there is a need in the art for an improved, repairable process of interconnecting two or more independent substrates.